JP3191842B2 - Production method of lactate ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a lactic acid ester from acetaldehyde and formate. Lactic acid esters are used in large quantities as solvents for the paint and electronics industries, as raw materials for organic synthesis such as pharmaceuticals, or as raw materials for various polymers such as acrylic resins and biodegradable polymers. It is an important chemical.

[0002]

2. Description of the Related Art As an industrial method for producing a lactic acid ester, a method is generally employed in which cyanhydrin is synthesized from hydrocyanic acid and acetaldehyde as raw materials, hydrolyzed, and then esterified. Other methods for producing lactic acid include a method of reacting dinitrogen tetroxide on the terminal olefin followed by hydrolysis, a method of reacting acetaldehyde with carbon monoxide or water in the presence of a noble metal catalyst or an acid catalyst, or a method of producing carboxylic acid. A method is known in which the α-position is halogenated and then hydrolyzed. These production methods are not suitable for large-scale industrial production of lactic acid, such as insufficient yield, limited raw material sources, cumbersome reactions and separation / purification operations, or expensive catalysts. It cannot be a simple production method and is currently used only for small-scale production of specific lactic acid and its derivatives.

[0003]

The current method of synthesizing cyanohydrin from hydrocyanic acid and acetaldehyde, its hydrolysis and esterification is widely practiced because of its easy reaction and high yield. However, this method has a disadvantage in that a large amount of ammonium salt is produced as a by-product, and this treatment puts pressure on the production cost of lactate ester.

[0004]

The present inventors have first found a method for producing methacrylic acid using acetone and methyl formate as raw materials and passing through acetone cyanohydrin but not producing ammonium salts as a by-product. (Japanese Patent Laid-Open No. 4-198152)
issue). In this method, it was found that lactate ester can be efficiently produced by using acetaldehyde instead of using acetone as a starting material, and completed the present invention. That is, the present invention provides (1) a step of producing lactonitrile by the reaction of hydrocyanic acid and acetaldehyde,
(2) a step of producing lactoamide by hydrating the cyanohydrin obtained in the above step, (3) a step of producing lactate ester and formamide from the lactoamide and formate ester obtained in the above step, and (4) the step of producing lactamide and formamide. And a process for producing and circulating hydrocyanic acid by dehydrating formamide separated from the resulting product. Although the method of the present invention is carried out via cyanohydrin, when viewed as a whole process, it is a process in which lactate ester can be finally produced using acetaldehyde and formate as raw materials. There is a characteristic that it is not accompanied by life at all.

Hereinafter, the method of the present invention will be described in detail. Acetaldehyde is industrially produced in large quantities at low cost from ethylene by oxidation as a solvent or as various chemical raw materials. On the other hand, methyl formate is produced on an industrial scale by a carbonylation method or a dehydrogenation method using methanol, which is produced in large quantities at low cost, as a raw material. Other formate esters can be easily produced by transesterification between methyl formate and alcohol. In the present invention, the production of cyanohydrin by the reaction of hydrocyanic acid and acetaldehyde is carried out by a known method, and is easily carried out at a low temperature of about 10 ° C. in the presence of a base catalyst such as an alkali metal hydroxide or an amine. Will be implemented.

The production of lactamide in the present invention is carried out by contacting a mixture of cyanohydrin and water in the presence of a catalyst. As the catalyst, a catalyst effective for the hydration reaction of nitriles can be used, and a strong acid such as sulfuric acid is also used. desirable. Specifically, manganese, copper, nickel or their oxides are effective, and manganese oxide is particularly preferred.
The charge weight ratio of cyanohydrin to water is 10:90.
90 to 10 is a suitable range. Also, in this system,
Acetaldehyde, alcohol, ketones such as acetone, which are raw materials of cyanohydrin, and the like can be used together as a solvent. When using manganese oxide as a catalyst, the reaction temperature is preferably in the range of 20 to 150 ° C, and particularly preferably 30 to 100 ° C. The reaction time is 0.
It is preferably from 3 to 6 hr, and particularly preferably from 0.5 to 3 hr. The reaction can be carried out in either a batch system or a continuous system.

In the present invention, the production of lactate ester and formamide by the reaction of lactoamide and formate can be carried out by heating a mixture of lactamide and formate without a catalyst, but in the presence of a solvent and a catalyst. It is effective to carry out in. When methyl formate is used as the formate, methanol and carbon monoxide can be used instead of methyl formate. This reaction is an equilibrium reaction, and the yield of lactic acid ester depends on the molar ratio of lactoamide to formate, and the formic ester / lactamide (molar ratio) to be charged is preferably from 1 to 10, particularly preferably from 2 to 5. It is. The addition of the solvent has the effect of increasing the solubility of the solid lactide and increasing the selectivity of the reaction. The solvent to be used is most preferably an alcohol corresponding to a formate, and the charged molar ratio of the alcohol to the lactoamide is preferably 1 to 10, particularly preferably 2 to 5.

As catalysts for this reaction, alkali metal alcoholates, oxides of alkaline earth metals, and strongly basic ion exchange resins are extremely excellent. Alkali metal alcoholates are synthesized from lithium, sodium, and potassium metals and lower alcohols, and specific examples include sodium and potassium methylates, ethylates, and butyrates. Examples of the alkaline earth metal oxide include magnesium oxide, calcium oxide, and barium oxide. The reaction conditions in the case of using an alkali metal alcoholate, an oxide of an alkaline earth metal, or a strongly basic ion exchange resin as a catalyst include a reaction temperature of 20 to 80 ° C. and a reaction time of 0.5 to 6 hr based on 1 mol of lactoamide. Catalyst usage 0.001-0.
30 mol is suitable. The reaction product in this step is
Separation and recovery are performed by operations such as distillation, and unreacted substances are returned to the raw material system. Formaldehyde produced simultaneously with the desired lactate ester is subjected to a dehydration reaction to produce hydrocyanic acid. The generated hydrocyanic acid is recovered, sent to a cyanohydrin production process and recycled.

[0009]

According to the present invention, each step proceeds at an extremely high selectivity, and finally a lactate ester can be produced in a high yield from acetaldehyde and a formate ester as raw materials. There are no undesirable by-products such as ammonium salts of

[0010]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited by these examples. Example 1 (Synthesis of methyl lactate) (1) Step (Synthesis of lactonitrile from hydrocyanic acid and acetaldehyde) Acetaldehyde 8 was placed in a 500-mL flask equipped with a stirrer, thermometer, reflux condenser, and dropping funnel.
8.1 g and 1 mL of a 1N aqueous sodium hydroxide solution were charged, and while maintaining the temperature in the flask at 10 ° C., hydrocyanic acid 5 was added.
9.4 g were added dropwise. After the addition of cyanuric acid, 2 hours at 20 ° C
and the reaction was completed. Next, the pH of the resulting solution was adjusted to 3 by adding 50% sulfuric acid. The flask was connected to a reduced pressure system, and unreacted hydrocyanic acid was removed from the system to obtain 142 g of lactonitrile. The purity of lactonitrile was 98.8%, and the yield of lactonitrile based on acetaldehyde was 98.7%.

(2) Step (Synthesis of Lactamide by Hydration of Lactonitrile) Preparation of Catalyst: 63.2 g of potassium permanganate and 500 g of water are placed in a 1-liter flask equipped with a stirrer, a reflux condenser and a thermometer. Was heated and stirred at 70 ° C. To this, 240 g of an aqueous solution in which 96.2 g of manganese sulfate was dissolved and 40 g of 15% sulfuric acid were added and reacted at 70 ° C. for 3 hours. After cooling the contents, the precipitate was filtered off with suction and washed with 2.4 L of water. The precipitate cake is dried at 60 ° C. for 24 hours, 74 g.
Was obtained and used as the following catalyst. Hydration reaction: 121 g of the lactonitrile obtained in step (1), 350 g of water, and 60 g of manganese dioxide were placed in a 1-L flask equipped with a stirrer, a reflux condenser, and a thermometer in order.
g was charged and reacted by heating and stirring at 60 ° C. for 5 hours. After the resulting solution was ice-cooled, the mixture was subjected to suction filtration to separate the catalyst. As a result of gas chromatographic analysis of the filtrate, the conversion of lactonitrile was 99.5%, and the yield of lactoamide was 9%.
7.5%. The filtrate was concentrated to dryness under reduced pressure to give lactoamide 148 having a purity of 99.5% or more as a main component.
g was obtained.

(3) Step (Synthesis of methyl lactate and formamide from lactoamide and methyl formate) In a 1 L stainless steel autoclave equipped with a stirrer, 44.5 g of lactoamide obtained in (2), 180 g of methyl formate, methanol 96 g and 1.1 g of sodium methylate were charged and reacted by heating and stirring at 60 ° C. for 2 hours. After cooling the product, gas chromatographic analysis showed that the conversion of lactamide was 86.1%, the selectivity of methyl lactate based on lactamide was 99.8%, and the selectivity of formamide was 98.4%. Was. After neutralizing the sodium methylate in the product solution with sulfuric acid, it is distilled by a conventional method to recover methyl formate and methanol,
40 g of methyl lactate having a purity of 99% or more and 14 g of formamide having a purity of 99% were obtained. The recovery including the middle distillate was quantitative.

(4) Step (Production of hydrocyanic acid by dehydration of formamide) Preparation of catalyst: To 51.5 g of manganese carbonate, 0.88 g of sodium carbonate dissolved in 30 g of water was added and kneaded for 1 hour. Then, it is dried at 110 ° C. for 15 hours, and 10% hydrogen-
Bake at 450 ° C for 5 hours in a stream of nitrogen, then crush
30 g of a mesh of 0 to 20 mesh was obtained. Reaction: 3.0 g of manganese oxide obtained by the above method was filled in a quartz reaction tube having an inner diameter of 10 mm x 300 mm equipped with a thermometer sheath tube, and heated so as to maintain the temperature at the lower portion of the catalyst layer at 400 ° C. Also, 3φ × 3m is placed on the upper 15cm of the catalyst layer.
The m-quartz Raschig ring was filled and heated to 100 to 400 ° C. to form a formamide evaporator. 100m inside the reaction tube
While maintaining a vacuum of mHg, the formamide obtained in (3) was introduced into the system from the top of the reaction tube at a rate of 10 g / hour and air at a rate of 240 ml / hour.

From 5 hours after the start of the reaction, the reaction gas was sampled for 1 hour. The hydrocyanic acid collected by absorption into water and an aqueous NaOH solution was quantified by silver nitrate titration. Ammonia dissolved in water was quantified by ion chromatography, and unreacted formamide was quantified by gas chromatography. As a result, the formamide conversion was 99.
The yield was 5%, the hydrocyanic acid yield was 95.2%, and the ammonia yield was 4.3%.

Example 2 Example 1 was repeated except that the raw material methyl formate was replaced with ethyl formate.
The reaction was carried out in the same manner as As a result, the reaction rate of lactamide was 86.1%, the selectivity of ethyl lactate on the basis of lactamide was 99.8%, and the selectivity of formamide was 98.4.
%Met.

Example 3 In the step (3) of Example 1, 200 g of methanol was charged in place of 180 g of methyl formate and 96 g of methanol, and 40 atm of carbon monoxide was injected, and the mixture was heated and stirred to react. When the temperature in the autoclave reaches 60 ° C,
Carbon monoxide was supplied so as to maintain the reaction pressure at 40 atm, and the reaction was continued for 3 hours. Thereafter, the temperature in the autoclave was cooled to 10 ° C., and the internal pressure was gradually lowered to normal pressure. The product was taken out and analyzed by gas chromatography. As a result, the reaction rate of lactoamide was 81.7%, based on lactoamide. The selectivity for methyl lactate was 95.9% and the selectivity for formamide was 94.8%.

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI // C07B 61/00 300 C07B 61/00 300 (56) References JP-A-5-178792 (JP, A) JP-A-4 -198152 (JP, A) JP-A-58-55444 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 1/00-409/44 CA (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] (1) a step of producing lactonitrile from hydrocyanic acid and acetaldehyde; (2) a step of hydrating the lactonitrile obtained in the above step to produce lactoamide; (3)
A step of producing lactate ester and formamide from the lactoamide and formate ester obtained in the step, and (4) a step of dehydrating formamide separated from the product obtained in the step to produce hydrocyanic acid and circulating and using the same. A method for producing a lactic acid ester represented by the following general formula: CH ₃ CH (OH) COOR (R: alkyl group having 1 to 8 carbon atoms). 2. The method according to claim 1, wherein the formate used in the step (3) is methyl formate. 3. The method according to claim 2, wherein in step (3), methanol and carbon monoxide are used in place of methyl formate.